1. Field of the Invention
This invention relates to hydrocarbon conversion catalysts, such as those utilized to catalyze the reaction of hydrogen with organo-nitro, organo-metallic and particularly organo-sulfur compounds. More particularly, this invention is directed to catalysts useful for the hydrodesulfurization of hydrocarbons and to a method for preparing such catalysts employing a novel aqueous impregnating solution. The invention is especially directed to catalysts of high overall desulfurization activity and stability.
2. Description of the Prior Art
In the refining of hydrocarbons, it is often necessary to convert a hydrocarbon fraction to different forms. In one such conversion, hydrodesulfurization, the concentration of sulfur components in a hydrocarbon feedstock is reduced so that, when the product is eventually combusted, less sulfur oxides will form, and hence will present fewer pollution problems. In addition, it is often desirable to remove sulfur from hydrocarbon fractions in order to protect catalysts used in subsequent processing steps which are rapidly deactivated in the presence of sulfur, and to otherwise render such sulfur-containing hydrocarbon fractions more useful.
The reaction of organo-sulfur compounds contained in hydrocarbon feedstocks with hydrogen is known to be accelerated in the presence of a catalyst comprising a Group VIB metal, a Group VIII metal, and phosphorus supported on a refractory inorganic oxide. Compositions containing these and other elements have been previously investigated. For example, hydrodesulfurization catalysts comprising a Group VIII metal, particularly cobalt or nickel, a Group VIB metal, particularly molybdenum or tungsten, and phosphorus on an alumina or silica-stabilized alumina base have been disclosed in U.S. Pat. Nos. 3,755,150, 3,755,196, and 3,840,472. Such catalysts are very often prepared by impregnation, that is, the deposition of the active components on the support base by contact thereof with an aqueous solution containing the active components in dissolved form. U.S. Pat. No. 3,755,196, for example, describes impregnating media and methods using stabilized impregnating solutions for preparing catalysts consisting of molybdenum plus nickel or cobalt salts with phosphoric acid dissolved in an aqueous medium. U.S. Pat. No. 3,840,472 discloses another process for preparing a stable impregnating solution that includes dissolving a nickel or cobalt compound with an acid of phosphorus followed by subsequent dissolution of molybdic oxide.
Although conventional catalysts are active and stable for hydrodesulfurization, catalysts of yet higher activities and stabilities are still being sought. Increasing the activity of a catalyst increases the rate at which a chemical reaction proceeds under given conditions, and increasing the stability of a catalyst increases its resistance to deactivation, that is, the useful life of the catalyst is extended. In general, as the activity of a catalyst is increased, the conditions required to produce a given end product, such as a hydrocarbon of given sulfur content, become more mild. Milder conditions require less energy to achieve the desired product, and catalyst life is extended such as due to lower coke formation.
It is believed in the prior art that greater active component uniformity in the catalytic particles improves activity. The formation of a more evenly distributed layer of the active components, such as the metals, and their oxides, or sulfides, in sufficient concentration through the entire surface area of the catalytic support provides more efficient utilization of the entire catalytic contacting surface at milder conditions for longer periods of time.
Accordingly, it is an object of this invention to provide hydrocarbon conversion catalysts having a relatively evenly distributed layer of active components and to provide a method for using such catalysts for the desulfurization of hydrocarbons. Another object is to provide a method for producing hydrocarbon conversion catalysts of improved desulfurization activity and stability in comparison to conventional catalysts of similar composition. Still another object is to provide hydrocarbon conversion catalysts of improved desulfurization activity and stability in comparison to conventional catalysts of similar composition. These and other objects and advantages of the invention will be apparent from the following description.